Cationic and Neutral PdII and PtII Pincer Complexes of Phosphinamino-Triazolyl-Pyridine [PN(H)N]: Pincer Ligand-Stabilized Palladium Nanoparticles and Their Catalytic Annulation of Internal Alkynes to Indenones

We describe the synthesis of a triazolyl-pyridine-basedaminophosphine, N-(diphenylphosphaneyl)-6-(1-phenyl)-1H-(1,2,3-triazol-4-yl)pyridine-2-amine [2,6-{(PPh2)-N(H)(C5H3N)(C2HN3C6H5)}] [1, PN(H)N hereafter], and itspalladiumand platinum complexes and their catalytic application. The reactionof 1 with [M(COD)Cl-2] (M = Pd or Pt) affordedthe cationic complex [(MCl){PN(H)N}-& kappa;(3)-P,N,N]Cl [M= Pd (2) or Pt (3)]. Alternatively, compounds 2 and 3 were also synthesized by treating [2,6-{H2N(C5H3N)(C2HN3C6H5)}] (A) with [M(COD)Cl-2] (M = Pd or Pt), followed by the addition of stoichiometricamounts of PPh2Cl and Et3N. The neutral, dearomatizedcomplexes [(MCl){PNN}-& kappa;(3)-P,N,N] [M = Pd (4) or Pt (5)] were prepared by the deprotonation of theNH of 2 and 3 with 1 equiv of (BuOK)-Bu- t . Compounds 4 and 5 were also synthesized stepwise by treating [2,6-{H2N(C5H3N)(C2HN3C6H5)}] (A) with [M(COD)Cl-2] (M = Pd orPt) to give intermediate complexes [{MCl2}2,6-{NH2(C5H3N)(C2HN3C6H5)-& kappa;(2)-N,N}] [M = Pd (B)or Pt (C)], which were subsequently phosphinated. The in situ-generated PNN ligand-stabilized Pd nanoparticlesfrom compound 2 catalyzed the annulation of o-bromobenzaldehyde with alkynes to yield indenone derivatives. Mechanisticinvestigations suggested that the reaction was catalyzed by Pd nanoparticles(Pd@2) generated from compound 2 and proceededthrough sequential oxidative addition, alkyne insertion, and reductiveelimination steps to produce indanone products. This paper describes the synthesis of palladium and platinumcomplexes of aminophosphine with a triazolyl-pyrdine functionalityand catalytic annulation of internal alkynes to indenones.

Automated summary

This study presents the synthesis of a triazolyl-pyridine-based aminophosphine compound and its Pd and Pt complexes, as well as their catalytic application in the annulation of internal alkynes to yield indenones. The results show that the Pd@2 catalyst generated from compound 2 can effectively catalyze the annulation reaction.